For some time it has been recognized that it would be desirable in many applications to eliminate the need for sewing in forming a fabric hem and to utilize an adhesive for securement of the hem. Various methods and devices have been proposed for this purpose, among which include the use of preformed beads or strips of adhesive which may be placed between the fabric layers and activated, as by heating, as well as the direct application of a molten hot melt adhesive to the fabric as disclosed in U.S. Patent Office Defensive Publication Numbers T926,006 and T926,010, published Sept. 3, 1974. However, the prior devices and methods for producing adhesively secured hems with which applicants are familiar all have significant problems or deficiencies which make them totally impractical, or at best, of limited usefulness in commercial applications.
More particularly, the prior methods and devices with which applicants are familiar have been unsuccessful in obtaining an adhesive bond of sufficient strength as to be commercially acceptable and capable of withstanding the handling and laundering encountered in normal use. Also, in the previously known devices and methods, significant production difficulties were presented in properly controlling the application of the adhesive to the fabric to avoid producing inferior or second quality products, as would result, for example from undesirable bleed-through of the adhesive to the visible surface of the fabric.
With the foregoing in mind, it is a primary object of the present invention to provide an effective and commercially practical method and apparatus for forming a hem in a fabric utilizing a hot melt adhesive for securement of the hem.
It is a further object of this invention to provide a method and apparatus of the type described which is capable of providing an adhesively secured hem having sufficient bond strength to withstand the handling and laundering encountered in normal use of the fabric.
It is a further object of this invention to provide a method and apparatus for forming an adhesively secured hem in a fabric capable of giving more effective and precise control over the penetration of the adhesive into the fabric in order to achieve enhanced and more uniform quality hems with a strong bond between the fabric layers and while avoiding undesirable bleed-through of the adhesive to the visible surface of the fabric.
It is still another object of this invention to provide a method and apparatus for forming an adhesively secured hem in a fabric and wherein the method and apparatus is especially suited for use in relatively heavy fabrics such as drapery fabrics and wherein the adhesively secured hem eliminates the puckers normally associated with a hem secured by sewing and thus produces a hem with greatly enhanced appearance over a conventionally sewn hem.
In the development work which led to the method and apparatus disclosed herein, it was learned that the poor bond strength observed when using a hot melt adhesive for securing fabric layers results not so much from the nature of the adhesive as from the manner of application of the adhesive. The hot melt adhesive used for securement of the fabric layers does not become significantly chemically bonded to the yarns or fibers, but rather the bonding results largely from a physical or mechanical attachment between the adhesive and the yarns or fibers. Where bond failure occurred, it was observed that the adhesive actually peeled away or separated from the fabric layer. In investigating this phenomenon further, it was determined that this failure was largely attributable to the adhesive becoming cooled and hardened or "crusted over" before it had an opportunity to penetrate into and between the yarns forming the fabric and to thereby become physically or mechanically secured to the fabric.
To overcome this problem the present invention provides for preheating the fabric to an elevated temperature prior to application of the molten adhesive thereto. This allows the hot melt adhesive to remain in a molten state for a longer period of time after application to the fabric so that the adhesive may penetrate into the fabric before hardening. The preheating of the fabric also provides an additional and effective control parameter which may be utilized alone, or in combination with other parameters such as application temperature of the adhesive, speed of advancement of the fabric, and amount of pressure applied, for precisely controlling the optimum penetration of the adhesive into the fabric.
In accordance with the present invention the fabric is continuously advanced along a predetermined path of travel while one longitudinal edge portion of the fabric is directed into and through a heating zone. The longitudinal edge portion of the fabric is heated to an elevated temperature and folded upon itself into overlying fabric layers to define a longitudinal hem along the edge of the fabric. A stream of hot melt adhesive is then applied between the overlying layers of the thus folded heated fabric, and immediately thereafter pressure is applied to the longitudinal hem to cause the adhesive to spread and penetrate into the fabric layers. During the application of pressure to the fabric, relative movement between the fabric layers is prevented until the adhesive sufficiently cools and hardens to secure the hem together.
The heating zone for heating the longitudinal edge portion of the fabric comprises an elongate heating chamber. The heating chamber preferably includes an elongate tubular member having a slit-like opening extending longitudinally thereof for receiving the longitudinal edge portion of the fabric interiorly of the tubular member with the remaining portions of the fabric located outside the tubular member. A hot air blower cooperates with the elongate tubular member for directing a current of heated air into and along the interior of the tubular member and into contact with the longitudinal edge portion of the fabric being directed through the tubular member.
In order to apply pressure to the hem and prevent relative movement of the fabric layers after application of the molten adhesive to the fabric, the apparatus of the present invention provides a pair of endless belts, with means mounting the belts for movement along respective elongate paths in opposing contacting relation with one another to define an elongate compression zone and therebetween for receiving and engaging the hem. More particularly, the means for mounting the pair of belts comprises respective sets of guide rolls for each belt and means for biasing the guide rolls of one set toward the corresponding guide rolls of the other set for applying pressure to the belts and to the hem positioned therebetween. The apparatus provides for adjusting the amount of pressure applied to the belts and to the hem positioned therebetween to thereby facilitate accurately controlling the amount of penetration of the molten adhesive into the fabric to prevent undesirable bleed-through of the adhesive to the visible surfaces of the fabric.
The apparatus and method of the invention also provide for receiving the advancing fabric upon the completion of the engagement and application of pressure to the adhesively secured hem and for directing the hem into and through an elongate cooling chamber while directing a current of air through the elongate cooling chamber and into contact with the hem for further cooling the adhesive to facilitate further handling of the fabric without disturbing the hem.
The method and apparatus of this invention are particularly well suited for continuously forming longitudinal hems in relatively heavy fabrics, such as drapery fabrics, such fabrics being generally formed from relatively coarse, soft twist yarns. However, the effective control over the adhesive application and penetration which can be achieved pursuant to this invention makes the method and apparatus of this invention useful with a broad range of fabrics of varying weight, construction, and texture.